Spark plug



J. A. DORAN Sept. 26, 1939.

SPARK PLUG Original Filed Oct. 4, 1932 INVENTOR JAMES ADUEAN d-Q; ATTORNEY Patented Sept. 26, 1939 UNITED STATES PATENT OFFICE Original application October 4, 1932, Serial No. 636,154, now Patent No. 2,164,311, dated July 4, 1939. Divided and this application May 24,

1939, Serial No. 275,490

6 Claims.

This invention relates to improvements in spark plugs and the present application is a division of application Serial Number 636,154, filed October 4, 1932.

An object of the invention is the provision in a spark plug of an outer shell having a stepped bore, the step of which forms a seat, an insulator retained in the bore in seated relation with the seat, and a sealing compound between a portion of the wall of said bore and an adjacent portion of the insulator.

Another object of the invention is the provision of a spark plug including an insulator and a shell, and a sealing compound between at least a portion of the interior of the shell and a corresponding area of the insulator to render the insulator practically free from all risk of cracking.

A further object of the invention is to provide in a spark plug a sealing compound between portions of the interior of the shell and adjacent portions of the insulator for producingsealing cohesion therebetween.

This offers several advantages among which are, that a more effective seal against the leakage of compressed. gases is obtained, and due to the intimate contact between the shell, the compound, and the poreclain or the like forming the insulator, the resistance to the transfer of heat from the insulator is greatly decreased. If the compound is omitted the rate of heat transfer is so low that the temperature of the insulator remains higher. than that of the shell and the insulator is liable to crack.

Referring to the drawing:

Figure 1 is a sectional elevation of a spark plug which, by way of illustration, shows one embodiment of the invention; and

Figure 2 is an enlarged fragmentary view of a portion of Figure 1 showing the compound between the inner wall of the shell and the porcelain.

In the application Serial Number 636,154 above referred to, the spark plugs claimed therein all have their insulators inserted via the bottoms of the shells.

However, in the present application the insulators are inserted via the tops of the shells. The shell 53, preferably made of steel, has an hexagonal portion 2|, and a threaded portion 22. The bore of the shell is straight as indicated at 26 and is bounded at its upper end, as viewed in the drawing, by a thin walled annulus 54 of steel which is preferably formed integral with the body of the shell 53.

A step 51 is formed within the shell 53 adjoining the straight bore 26. In Figure 1, this step is shown as tapered and forms a seat for the insulator to presently be described. I am not limited to the use of a tapered seat as in other arrangements a straight shoulder or seat (at sub stantially right angles with the bore) might be preferable.

Adjoining the seat 57 is a bored portion 3! smaller in diameter than the bore 26. A third bore 24 extends into the shell 53 from the threaded end and communicates with the bore 3|.

An insulator 55 has a tapered seating portion 56 which is seated upon the seat'5l, a tapered tip 59 which extends into the bore 24, and an inwardly sloping tapered portion 58 upon which the thin walled annulus 54 is rolled or spun. Prior to assembly a sealing compound is used to thoroughly seal the space between the engaging surfaces. One method of applying the compound is to coat the surface or surfaces of the insulator where sealing is desired and place the insulator in the shell and perform the rolling operation. If a suflicient quantity of compound is used the annulus while being rolled or spun down exerts pressure upon the compound causing it to establish intimate contact with the shell and the porcelain or other material of which the insulator is made. The compound is designated by the numeral 60.

The central bore of the insulator 55 carries an electrode 35. This electrode has a firing point 36 on its lower end and a conical flange 3'! which seats in a countersunk end of the insulator bore. The upper end 38 of the electrode is threaded to receive a lock nut 39 having a depending knurled portion 40 which seats firmly in a recess 34 formed in the top end of the insulator. A suitable terminal 4| is carried on the threaded upper end 38 of the electrode.

Before the electrode is inserted in the insulater, the conical flange 31 and the countersunk seat are coated with sealing compound. After the electrode is inserted, some sealing compound is placed in the recess 34 in the top of the insulator so that when the locking nut 39 is firmly screwed down the conical flange is firmly seated in sealed relation to the countersunk seat in the bottom of the insulator and the knurled depending portion 40 of the lock nut is sealed and locked in place in the top of the insulator.

The lower end of the shell is provided with a downwardly projecting annular portion 43 spaced from the bore 24 to form a shoulder against which an electrode plate 45 is positioned or located. By folding over or spinning the annular portion 43, the electrode plate is positively maintained on the lower end of the shell in electrically conductive relation thereto.

The electrode plate has a central opening through which the firing point 36 extends, and a plurality of radially spaced prongs or tines 46 form the innermost boundaries of said central opening, and form with the firing point 35, a plurality of spark gaps.

The lengths of the gaps may be adjusted by bending the tines 46. This structure greatly prolongs the life of the plug and facilitates combustion, as the spark will first begin jumping the shortest gap, then as the metal burns away will begin jumping the next shortest gap, etc.,continuing indefinitely, so that the tines all gradually burn away, thereby greatly prolonging the life of the plug.

Although a single embodiment of the invention is herein described employing a sealing compound between portions of the inner wall of a spark plug shell and the insulator for sealing the plug against leakage and for increasing the heat conductivity from the porcelain to the shell, it

is obvious that many changes may be made in the relation of the elements and the compound without departing from the spirit of the invention as defined in the annexed claims.

What is claimed is:

1. In a spark plug, a body having a cylindrical bore and forming a shell, said bore being stepped to form an annular shoulder therein, an insulator mounted in said body and having a portion thereof seating on said shoulder, said insulator having a terminal end extending upwardly from said shell and a tapered firing end near the bottom of said shell, means on said body made effective after said insulator is mounted therein for retaining said insulator in said body, and a sealing compound forming a bond between at least a portion of the length of the wall of said bore and a corresponding portion of said insulator.

2. In a spark plug, a shell externally threaded far mounting on an engine and having a bore extending therethrough, an upwardly facing seat formed in said bore, an insulator in said bore having a downwardly facing surface substantially parallel to said seat, said insulator having a terminal end extending upwardly from said shell and a tapered firing end near the bottom of said shell, a thin tubular boss on said shell adapted to be spun over for retaining said insulator in said shell, and a layer of sealing compound within said shell adapted to be placed under pressure by the spinning over of said boss for effecting a bond between a portion of said shell and a corresponding portion of said insulator.

3. A spark plug according to claim 2 in which said sealing compound in addition to effecting a bond between said portions,also extends between said upwardly facing seat and said downwardly facing surface for effecting a seal therebetween.

4. In a spark plug, a body having a cylindrical bore and forming a shell, said bore being stepped to form an annular shoulder therein, an insulator mounted in said body and having a portion thereof seating on said shoulder, said insulator having a terminal end extending upwardly from said shell and a tapered firing end near the bottom of said shell, means on said body made effective after said insulator is mounted therein for retaining said insulator in said body, and a sealing and bonding compound between a portion of said bore and a corresponding portion of said insulator, and confined therebetween by said means.

5. In a spark plug, a shell externally threaded for mounting on an engine and having a bore extending therethrough, an upwardly facing seat formed in said bore, an insulator in said bore having a downwardly facing surface substantially parallel to said seat, said insulator having a terminal end extending upwardly from said shell and a tapered firing end near the bottom of said shell, means on said shell made effective after said insulator is mounted therein for retaining said insulator in said shell, and a layer of sealing compound between said shell and said insulator bounded by said retaining means and said seat.

6. In the manufacture of spark plugs, the method of mounting and sealing an insulator member in a shell member which consists in providing a sealing compound, placing said insulator and said compound in said shell with said insulator seating therein, and spinning or turning over an upper edge of said shell to bear upon said compound to force the latter into crevices between the insulator and the shell and thereby confining the compound under pressure within said shell.

JAMES A. DORAN. 

